JP2015218327A - Polylactic acid resin composition for injection foam, injection foamed body and manufacturing method of injection foamed body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic acid resin composition capable of efficiently providing an injection foamed body having excellent heat resistance and good strength and an injection foamed body using the resin composition.SOLUTION: There is provided a polylactic resin composition for injection foaming mainly containing a polylactic resin (A) having a D body content of 2 mol% or less and satisfying following conditions (1) to (3) at the same time. (1) Melt viscosity measured at 190°C is 20 to 200 mN. (2) Melting viscosity (MFR-1) measured under the condition at 190°C and 21.6 N is 0.1 to 20 g/10 min. and a ratio to melting viscosity (MFR-2) measured under the condition at 190°C and 132.25 N, (MFR-2/MFR-1), is 15 or more. (3) A ratio between slope of linear area in an elongation initial stage until the appearance of an inflection point, a1, and slope of elongation latter stage after the inflection point, a2, in a time-elongation viscosity curve obtained by an elongation viscosity measurement at a temperature higher than the melting point by 10°C, (a2/a1, distortion curing coefficient) is 1.2 to 20.

Description

  The present invention relates to a polylactic acid-based resin composition for obtaining an injection-foamed molded article having a low environmental impact and having a low environmental impact as a main component, light weight, and excellent mechanical properties and heat resistance. The present invention relates to an injection foam molded article using the resin composition.

  Conventionally, a technique for obtaining a thermoplastic resin foam by impregnating or dissolving a gas in a thermoplastic resin and then degassing it has been widely used, and the obtained foam has been used in various applications.

  In recent years, however, thermoplastic foams that are used in large quantities and then disposed of in large quantities have a great impact on the environment during use and disposal, and have various problems such as global warming, resource depletion, and waste disposal. It is a cause of social problems.

  Therefore, various foams of polylactic acid resin have been proposed from the viewpoint that they have a low environmental load, can be produced at a relatively low cost, and exhibit biodegradability (see, for example, Patent Document 1). However, the polylactic acid resin has a very low crystallization rate, is in an amorphous state after molding unless a mechanical process such as stretching is performed, and the glass transition temperature of the polylactic acid resin is about 60 ° C. Application to applications was limited.

  In order to improve the heat resistance of the polylactic acid resin, it is important to crystallize at the time of molding. For example, a production method in which polylactic acid is crystallized using a supercritical fluid in injection molding has been proposed ( For example, Patent Document 2). However, this method has a drawback in that the apparatus and process are complicated because the supercritical fluid is injected during the injection molding.

JP 2000-136255 A JP 2003-236944 A

  The present invention solves the above-described problems, and a polylactic acid-based resin composition capable of efficiently obtaining an injection foam molded article having excellent heat resistance and good strength, and the resin composition An object of the present invention is to provide an injection-foamed molded article using a product.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have reached the present invention.
That is, the gist of the present invention is as follows.
(A) A polylactic acid resin composition for injection foaming, characterized in that the main component is a polylactic acid resin (A) having a D-form content of 2 mol% or less, and simultaneously satisfies the following conditions (1) to (3): object.
(1) The melt tension measured at 190 ° C. is 20 to 200 mN. (2) The melt viscosity (MFR-1) measured at 190 ° C. and 21.6 N is 0.1 to 20 g / 10 min. The ratio (MFR-2 / MFR-1) to the melt viscosity (MFR-2) measured under conditions of 190 ° C and 132.25N is 15 or more.
(3) In the time-elongation viscosity curve obtained by the extensional viscosity measurement at a temperature 10 ° C. higher than the melting point, the slope a1 of the linear region at the initial stage of elongation until the inflection point appears and the slope a2 of the later stage of elongation after the inflection point The ratio (a2 / a1, strain hardening coefficient) is 1.2-20.
(B) The polylactic acid resin composition for injection foaming according to (a), wherein the crystallization rate index is 0.1 to 10 (min).
(C) The crystal nucleating agent (B) is contained in an amount of 0.5 to 50 parts by mass with respect to 100 parts by mass of the polylactic acid resin (A) having a D-form content of 2 mol% or less. B) is at least one selected from talc, silica, layered silicate, glass fiber, and organic crystal nucleating agent, and the polylactic acid-based resin composition for injection foaming according to (a) or (b) object.
(D) An injection foam molding comprising the polylactic acid resin composition for injection foam according to any one of (a) to (c), and an apparent density of 1.1 g / cm ³ or less. body.
(E) 0.01 to 2 parts by mass of the foaming agent (C) is added to 100 parts by mass of the polylactic acid-based resin composition for injection foaming according to any one of (i) to (c), A method for producing an injection foam molded article, comprising performing injection molding.

In the present invention, since the polylactic acid resin (A) having a D-form content in a specific range is used, the crystal performance is improved by improving stereoregularity, and the heat resistance and moldability are remarkably improved. A lactic acid resin composition can be obtained. Furthermore, the polylactic acid-based resin composition of the present invention has excellent foamability, low specific gravity, excellent strength, and heat resistance by making melt tension, melt viscosity, elongation viscosity, etc. within a specific range. It is possible to obtain a foamed molded product efficiently. And since the polylactic acid-type resin composition of this invention uses the resin derived from a natural product, it can contribute to the saving of depletion resources, such as petroleum, and its industrial utility value is very high.
In addition, the injection-foamed molded article using the polylactic acid-based resin composition of the present invention is excellent in foamability and formed with a large number of fine bubbles, so that it has a low specific gravity and high strength. Because of its excellent properties, it can be suitably used for various applications such as electrical and electronic equipment parts and miscellaneous goods.

  Hereinafter, the present invention will be described in detail. First, the polylactic acid resin (A) will be described. The polylactic acid resin (A) needs to have a D-form content of 2.0 mol% or less. Especially, it is preferable that it is 1.5 mol% or less, Furthermore, it is preferable that it is 1.0 mol% or less, and it is most preferable that it is 0.6 mol% or less.

  When the D-form content is within this range, the crystallinity is excellent. That is, not only the crystallization speed is high and the moldability is excellent, but also the crystallization is sufficiently easy to proceed, so that a molded body excellent in heat resistance can be obtained.

  When the polylactic acid resin has a D-form content outside this range, as described later, even if a cross-linked structure is introduced into the polylactic acid resin or a crystal nucleating agent (B) is contained, the crystallinity and heat resistance are increased. Both are difficult to improve sufficiently.

  In the present invention, the D-form content of the polylactic acid resin (A) is a ratio (mol%) occupied by the D lactic acid unit in the total lactic acid units constituting the polylactic acid resin (A). Therefore, for example, in the case of a polylactic acid resin (A) having a D-form content of 1.0 mol%, the polylactic acid resin (A) has a proportion of 1.0 mol% of D lactic acid units, and L lactic acid The proportion of units is 99.0 mol%.

  In the present invention, the D-form content of the polylactic acid resin (A) is, as will be described later in the Examples, methylated all of L-lactic acid and D-lactic acid obtained by decomposing the polylactic acid resin (A), It is calculated by a method of analyzing the methyl ester of L lactic acid and the methyl ester of D lactic acid with a gas chromatography analyzer.

  As polylactic acid resin (A) used for this invention, polylactic acid resin of the range which D body content prescribes | regulates by this invention among various commercially available polylactic acid resins can be used. In addition, among lactides, which are cyclic dimers of lactic acid, L-lactide having a sufficiently low D-form content or D-lactide having a sufficiently low L-form content is used as a raw material, and a known melt polymerization method is used. Alternatively, those produced by further using a solid phase polymerization method can be used.

  The polylactic acid resin (A) used in the present invention preferably has a weight average molecular weight of 50,000 to 300,000, more preferably 70,000 to 200,000, and more preferably 80,000 to 150,000. It is preferable that. When a polylactic acid resin having a weight average molecular weight of less than 50,000 is used, the resulting molded article tends to have insufficient mechanical strength. On the other hand, when the weight average molecular weight exceeds 300,000, the viscosity is too high, so that the processability is inferior, such as poor fluidity during injection foam molding. Moreover, it may be difficult to produce a resin composition having desired viscosity characteristics.

  In the present invention, as described later, the polylactic acid resin (A) preferably has a crosslinked structure introduced in order to improve foaming performance. In order to introduce a cross-linked structure and facilitate adjustment of melt viscosity, the polylactic acid resin (A) preferably has a weight average molecular weight within the above-mentioned range, and more preferably 70,000 to 200,000. It is preferable that it is 80,000 to 150,000.

  As a method for introducing a crosslinked structure into the polylactic acid resin (A), it is preferable to employ a method of blending a peroxide as a crosslinking agent and a crosslinking aid. Among these, it is preferable to use a (meth) acrylic acid ester compound as a crosslinking agent.

  As the (meth) acrylic acid ester compound, two or more (meth) acrylic compounds are contained in the molecule because of its high reactivity with polylactic acid resin, less monomer residue, relatively low toxicity, and little resin coloring. Compounds having a group or having one or more (meth) acryl groups and one or more glycidyl groups or vinyl groups are preferred. Specific compounds include glycidyl methacrylate, glycidyl acrylate, glycerol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, allyloxy polyethylene glycol monoacrylate, allyloxy polyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol. Diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol diacrylate, polytetramethylene glycol dimethacrylate, and these alkylene glycols may be copolymers of alkylenes of various lengths, but also butanediol methacrylate, butanediol acrylate, etc. Can be mentioned.

  The compounding amount of the (meth) acrylic acid ester compound is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of the polylactic acid resin (A). If it is less than 0.01 part by mass, it is difficult to obtain the intended effect of improving the melt viscosity. On the other hand, if it exceeds 20 parts by mass, the degree of cross-linking becomes too strong, and the operability is impaired.

  As the crosslinking aid, an organic peroxide having good dispersibility is preferable. Specifically, benzoyl peroxide, bis (butylperoxy) trimethylcyclohexane, bis (butylperoxy) cyclododecane, butylbis (butylperoxy) ) Valerate, dicumyl peroxide, butyl peroxybenzoate, dibutyl peroxide, bis (butylperoxy) diisopropylbenzene, dimethyldi (butylperoxy) hexane, dimethyldi (butylperoxy) hexyne, butylperoxycumene, triethyl-trimethyl -Tripperoxonan etc. are mentioned. Among them, it is particularly preferable to select from dibutyl peroxide or triethyl-trimethyl-triperoxonan. It is preferable that the compounding quantity of a crosslinking adjuvant is 0.1-5 mass parts with respect to 100 mass parts of polylactic acid resin (A). If it is less than 0.1 parts by mass, it is difficult to obtain the intended effect of improving the melt viscosity. .

  The injection-foaming polylactic acid resin composition of the present invention (hereinafter sometimes simply referred to as a polylactic acid resin composition) satisfies the following conditions (1) to (3) at the same time. This makes it possible to obtain a good foam having a high expansion ratio and a uniform cell diameter.

First, the polylactic acid resin composition of the present invention has a melt tension value measured at 190 ° C. of 20 to 200 mN as the characteristic value of (1), preferably 40 to 170 mN, and preferably 60 to 150 mN. More preferably. When the melt tension is less than 20 mN, the resin is cut or torn when injection foam molding is performed, so that the foam molded body has a large cell diameter.
On the other hand, when the melt tension exceeds 200 mN, when injection foam molding is performed, since the resin does not stretch, bubbles do not grow, and the resulting molded product has a low foaming ratio. In addition, molding fluidity may be significantly reduced.

  The melt tension in the present invention is measured as follows. The measurement is performed using a Capillograph 1C manufactured by Toyo Seiki Seisakusho (cylinder inner diameter 9.55 mm, orifice inner diameter 1.0 mm, length 10.0 mm). First, the set temperature of the cylinder and the orifice is set to 190 ° C., the polylactic acid resin composition (measurement sample) is filled in the cylinder, and left for 5 minutes, and then the molten resin at 190 ° C. with a piston speed of 10 mm / min. Is extruded into a strand from the orifice. The strand is wound while passing through a circular guide of a tension detection pulley having a lower diameter of 40 mm, and a load applied to the circular guide is detected by a tensiometer. The winding speed is gradually increased, and the tension at which the strand breaks (that is, the maximum measurable tension) is taken as the melt tension.

  Furthermore, the polylactic acid resin composition of the present invention satisfies the characteristic value of (2). In other words, the melt viscosity (MFR-1) measured at 190 ° C. and 21.6 N is required to be 0.1 to 20 g / 10 minutes, and in particular, 0.2 to 18 g / 10 minutes. Is more preferable, and 0.5 to 15 g / 10 min is further preferable. When MFR-1 exceeds 20 g / 10 min, it does not have sufficient viscosity, so that foam breakage tends to occur at the time of injection foam molding, and closed cells are not sufficiently formed. It is inferior in mechanical strength. On the other hand, if the MFR-1 is less than 0.1 g / 10 min, the viscosity becomes too high, so that the fluidity is poor, the flow to the mold is poor at the time of injection foam molding, and an injection foam molded article is obtained efficiently. I can't. Further, since the viscosity is high, the foam cannot be sufficiently foamed, and it becomes difficult to obtain a foamed molded product having a small specific gravity.

And ratio (MFR-2 / MFR-1) of melt viscosity (MFR-2) measured on 190 degreeC and 132.25N conditions and MFR-1 is 15 or more, and it is 17 or more especially It is preferable that it is 20 or more.
Both MFR-1 and MFR-2 are measured according to JIS K-7210.

  The value of MFR-2 / MFR-1 is also a measure of the molecular weight distribution and linear branching of the resin composition. The higher the value of MFR-2 / MFR-1, the wider the molecular weight distribution and the higher the linear branching. Thus, a foam having a high expansion ratio can be obtained stably and stably. If the value of MFR-2 / MFR-1 is less than 15, the resulting foam tends to have a low foaming ratio. The upper limit of the value of MFR-2 / MFR-1 is preferably about 40 in order to obtain a good foam without bubble breakage.

  Furthermore, the polylactic acid resin composition of the present invention satisfies the characteristic value of (3). That is, in the logarithmic plot of time-extension viscosity (see FIG. 1) obtained by measuring the extension viscosity at a temperature 10 ° C. higher than the melting point of the resin composition (see FIG. 1), the slope a1 and the bend of the linear region at the beginning of extension until the inflection point appears. The strain hardening coefficient represented by the ratio (a2 / a1) to the slope a2 in the later stage of elongation after the point is 1.2 to 20, preferably 1.3 to 15, and preferably 1.5 to 10 More preferably it is.

  When the strain hardening coefficient is less than 1.2, foam breakage tends to occur during injection foam molding, so that the expansion ratio is limited, or excellent physical properties cannot be expressed by foam breakage. On the other hand, when the strain hardening coefficient exceeds 20, gel is likely to be generated during molding, the appearance of the resulting molded article is deteriorated, and the fluidity is greatly reduced, so that the operability is also inferior.

  The polylactic acid resin composition of the present invention preferably has a crystallization rate index of 0.1 to 10 (min). The crystallization rate index in the present invention is a differential scanning calorimeter (DSC apparatus “DSC7” manufactured by PerkinElmer Co., Ltd.), and the temperature is raised from 20 ° C. to 200 ° C. (+ 500 ° C./min), and then 5 at 200 ° C. When the temperature is lowered at 200 ° C. → 130 ° C. (−500 ° C./min) and then crystallized by holding at 130 ° C., the final degree of crystallinity is 1, and the crystallinity is 0 The time to reach 5 is defined as the crystallization rate index (minutes). The smaller the index, the faster the crystallization speed.

  When the crystallization rate index is higher than 10 (minutes), it is difficult to obtain a foamed molded article that is sufficiently crystallized by a normal injection foaming method and excellent in mechanical strength and heat resistance. On the other hand, when the crystallization rate index is smaller than 0.1 (min), the crystallization rate is too high, and it is difficult to obtain a foamed molded product having a small specific gravity by sufficiently foaming. The crystallization rate index is preferably 0.1 to 8 (minutes), more preferably 0.1 to 6 (minutes).

  In the polylactic acid resin composition of the present invention, the following crystal nucleating agent (B) can be used in order to appropriately adjust the above characteristic values. As the crystal nucleating agent (B) in the present invention, either an organic crystal nucleating agent or an inorganic crystal nucleating agent can be used.

  Examples of the inorganic crystal nucleating agent include talc, tin oxide, smectite, bentonite, dolomite, sericite, feldspar powder, kaolin, mica, montmorillonite and the like. Among these, talc is preferable from the viewpoints of improving the crystallization speed and heat resistance.

  Specific compounds that can be used as the organic crystal nucleating agent are selected from organic amide compounds, organic hydrazide compounds, carboxylic acid ester compounds, organic sulfonates, phthalocyanine compounds, melamine compounds, and organic phosphonates. It is preferable to use one or more selected from the above. Of these, organic sulfonates and organic amide compounds are preferred from the viewpoint of crystallization speed.

  As the organic sulfonate, various compounds such as sulfoisophthalate can be used, and among them, dimethyl metal salt of 5-sulfoisophthalic acid is preferable from the viewpoint of the effect of promoting crystallization. Furthermore, barium salt, calcium salt, strontium salt, potassium salt, rubidium salt, sodium salt and the like are preferable. Examples of commercially available products include LAK403 manufactured by Takemoto Yushi Co., Ltd.

  As the organic amide compound, various compounds can be used. Among them, N, N ', N "-tricyclohexyltrimesic acid amide, N, N'- is preferred from the viewpoint of dispersibility in the resin and heat resistance. Ethylene bis (12-hydroxystearic acid) amide is preferred, and examples of commercially available products include AS-AT-530SF manufactured by Ito Oil Co., Ltd.

  The content of the crystal nucleating agent (B) is preferably 0.1 to 50 parts by mass, more preferably 0.5 to 40 parts by mass with respect to 100 parts by mass of the polylactic acid resin (A). Especially, it is preferable to set it as 0.5-30 mass parts. When the content of the crystal nucleating agent (B) is less than 0.1 parts by mass, the effect as a crystal nucleating agent is small, and it is particularly difficult to lower the crystallization rate index. On the other hand, when it exceeds 50 parts by mass, the effect as a crystal nucleating agent is saturated, which is not only economically disadvantageous, but also increases the residue after biodegradation, which is not preferable in terms of environment. Furthermore, the apparent density of the resin composition may increase, and the resulting foamed molded product has a low expansion ratio (a high apparent density).

  The polylactic acid resin composition of the present invention preferably contains a carbodiimide compound in order to significantly improve wet heat durability.

  Various compounds can be used as the carbodiimide compound. As specific compounds, N, N′-di-2,6-diisopropylphenylcarbodiimide, N, N′-di-o-tolylcarbodiimide, N, N′-diphenylcarbodiimide, N, N′-dioctyldecylcarbodiimide, N, N'-di-2,6-dimethylphenylcarbodiimide, N-tolyl-N'-cyclohexylcarbodiimide, N, N'-di-2,6-di-tert-butylphenylcarbodiimide, N-tolyl-N ' -Phenylcarbodiimide, N, N'-di-p-nitrophenylcarbodiimide, N, N'-di-p-aminophenylcarbodiimide, N, N'-di-p-hydroxyphenylcarbodiimide, N, N'-di- Cyclohexylcarbodiimide, N, N'-di-p-tolylcarbodiimide, p-phenylene-bis-di-o-to Carbodiimide, p-phenylene-bis-dicyclohexylcarbodiimide, hexamethylene-bis-dicyclohexylcarbodiimide, ethylene-bis-diphenylcarbodiimide, N, N'-benzylcarbodiimide, N-octadecyl-N'-phenylcarbodiimide, N-benzyl-N '-Phenylcarbodiimide, N-octadecyl-N'-tolylcarbodiimide, N-cyclohexyl-N'-tolylcarbodiimide, N-phenyl-N'-tolylcarbodiimide, N-benzyl-N'-tolylcarbodiimide, N, N'- Di-o-ethylphenylcarbodiimide, N, N'-di-p-ethylphenylcarbodiimide, N, N'-di-o-isopropylphenylcarbodiimide, N, N'-di-p-isopropylphenylcarbodiimide Diimide, N, N'-di-o-isobutylphenylcarbodiimide, N, N'-di-p-isobutylphenylcarbodiimide, N, N'-di-2,6-diethylphenylcarbodiimide, N, N'-di- 2-ethyl-6-isopropylphenylcarbodiimide, N, N'-di-2-isobutyl-6-isopropylphenylcarbodiimide, N, N'-di-2,4,6-trimethylphenylcarbodiimide, N, N'-di -2,4,6-triisopropylphenylcarbodiimide, N, N'-di-2,4,6-triisobutylphenylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, di- β-naphthylcarbodi De, and the like di -t- butyl carbodiimide

  Among these compounds, those commercially available include, for example, monocarbodiimide having one carbodiimide group in the same molecule, such as EN-160 manufactured by Matsumoto Yushi Co., Ltd. Examples thereof include polycarbodiimide having two or more carbodiimide groups in the same molecule, such as EN-180 manufactured by Yushi Co., Ltd., Stavacsol P manufactured by Rhein Chemie, and Carbodilite LA-1 manufactured by Nisshinbo Industries, Ltd.

  Among them, monocarbodiimide has a high effect of improving the wet heat durability of polylactic acid resin, and it is particularly preferable to use N, N′-di-2,6-diisopropylphenylcarbodiimide. Examples of such commercially available monocarbodiimides include EN160 manufactured by Matsumoto Yushi Co., Ltd. and Stavacsol I manufactured by Rhein Chemie.

  The content of the carbodiimide compound is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the polylactic acid resin (A). Especially, it is preferable that it is 0.3-8.0 mass parts, and it is more preferable that it is 0.5-5.0 mass%. When the content of the carbodiimide compound is less than 0.1 parts by mass, it is difficult to obtain the effect of improving the wet heat durability as described above. On the other hand, when the content of the carbodiimide compound exceeds 10 parts by mass, not only the effect is saturated but also other physical properties such as strength reduction are adversely affected.

  Furthermore, the polylactic acid resin composition of the present invention may contain other resins than the polylactic acid resin (A) as a resin component as long as the effects are not impaired. Examples thereof include polyamide, polyolefin polyester, polystyrene, AS (acrylonitrile-styrene) resin, ABS (acrylonitrile-butadiene-styrene) resin, poly (acrylic acid), poly (acrylic acid ester), polyethylene naphthalate, and the like.

  In addition, the polylactic acid-based resin composition of the present invention includes a plasticizer, a heat stabilizer, an antioxidant, an organic filler, a pigment, a weathering agent, a flame retardant, a lubricant, a release agent, and the like within a range not impairing the effects of the present invention. Additives such as molds and antistatic agents can be added.

  As the plasticizer, polyester plasticizers, glycerin plasticizers, polycarboxylic acid ester plasticizers, phosphate ester plasticizers, polyalkylene glycol plasticizers, epoxy plasticizers, and the like can be used.

Examples of heat stabilizers and antioxidants include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, alkali metal halides, and vitamin E.
Examples of the organic filler include naturally occurring polymers such as starch, cellulose fine particles, wood flour, okara, fir shell, bran, kenaf, and modified products thereof.

As the flame retardant, a halogen-based flame retardant, a phosphorus-based flame retardant, and an inorganic flame retardant can be used. However, in consideration of the environment, it is desirable to use a non-halogen flame retardant. Non-halogen flame retardants include phosphorus flame retardants, hydrated metal compounds (aluminum hydroxide and magnesium hydroxide), N-containing compounds (melamine and guanidine), and inorganic compounds (borate and Mo compounds). It is done.
As the lubricant, various carboxylic acid compounds can be used, and among them, various fatty acid metal salts, particularly magnesium stearate, calcium stearate and the like are preferable.
As the release agent, various carboxylic acid compounds, among them, various fatty acid esters, various fatty acid amides, and the like are preferably used.

  Next, the manufacturing method of the polylactic acid-type resin composition of this invention is demonstrated. The polylactic acid-type resin composition of this invention can be obtained by supplying each component which comprises a resin composition in an extruder, and melt-kneading. However, since it is preferable that the crosslinking agent, the crosslinking assistant, the crystal nucleating agent (B) and the additive (carbodiimide compound, etc.) used as necessary are contained in the polylactic acid resin (A), these agents It is preferable to employ a method of adding a polylactic acid during polymerization of the polylactic acid resin (A), a method of adding these agents to the polylactic acid resin (A) in advance, and melt-kneading.

  In addition, in the case of the method of adding at the time of polymerization of the polylactic acid resin (A), a vertical reactor or a horizontal reactor equipped with a helical ribbon blade, a high-viscosity stirring blade or the like is used as a reaction vessel for performing melt ring-opening polymerization. Can be used alone or in parallel. In addition, the reaction vessel may be a continuous type, a batch type or a semi-batch type, or a combination thereof.

  In the case of the method of adding by melt-kneading in advance to the polylactic acid resin (A), after dry-blending with the polylactic acid resin (A) in advance, a method of supplying to a general kneader or molding machine, The method of adding from the middle of melt-kneading using a side feeder is mentioned.

  In melt kneading, a general kneader such as a single screw extruder, a twin screw extruder, a roll kneader, or a Brabender can be used. From the viewpoint of improving mixing uniformity and dispersibility, it is preferable to use a twin screw extruder.

  Next, the injection foam molded article of the present invention will be described. The injection-foamed molded article of the present invention uses the polylactic acid resin composition of the present invention. That is, the injection-foamed molded article of the present invention is formed using at least a part of the polylactic acid-based resin composition of the present invention, and is preferably composed of the polylactic acid-based resin composition of the present invention. .

  The injection-foamed molded article of the present invention preferably has a crystallinity of 5% or more, and particularly preferably a crystallinity of 10% or more. When the degree of crystallinity is less than 5%, the heat resistance becomes insufficient, and shrinkage may occur when secondary crystallization such as annealing is performed.

Here, the degree of crystallinity of the injection-foamed molded article is measured using a differential scanning calorimeter (DSC) while raising the temperature at a rate of temperature increase of 20 ° C./min according to the measurement method described in JIS K7121. The crystallinity is calculated from the following equation based on the temperature rise crystallization heat (ΔHc) and the crystal melting heat (ΔHm).
Crystallinity = [(| ΔHm | − | ΔHc |) / 93] × 100 (J / g)

The injection foam molded body of the present invention preferably has an apparent density of 1.1 g / cm ³ or less, more preferably 0.90 g / cm ³ or less, and 0.75 g / cm ³ or less. Is more preferable, and is most preferably 0.65 g / cm ³ or less. When the apparent density exceeds 1.1 g / cm ³ , the weight cannot be reduced because foaming is insufficient.

The apparent density of the injection-foamed molded article of the present invention is measured as follows.
First, the masses of the injection-foamed molded articles are measured, and then their apparent volumes are measured using a wet electronic hydrometer (“EW-300SG” manufactured by Alpha Mirage). The apparent density is calculated from the mass and the apparent volume.

Next, the manufacturing method of the injection foaming molding of this invention is demonstrated. The manufacturing method of the injection-foamed molded article of the present invention includes 0.01 to 2 parts by mass of the foaming agent (C) with respect to 100 parts by mass of the above-described polylactic acid resin composition for injection foaming of the present invention. The injection molding is performed.
Examples of the foaming agent (C) used in the present invention are pyrolysis-type organic compounds containing decomposable groups such as azo, N-nitroso, heterocyclic nitrogen-containing and sulfonyl hydrazide groups, ammonium carbonate, Inorganic compounds such as sodium bicarbonate can be used. Specific examples thereof include azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, diazoaminobenzene, dinitrosopentamethylenetetramine, N, N′-dimethyl-N, N′-dinitrosotephthalamide, benzenesulfonyl Hydrazide, 4,4′-oxy-bis (benzenesulfonyl) hydrazide, diphenylsulfone-3,3′-disulfonylhydrazide, 4-toluenesulfonyl hydrazide, 4,4′-oxy-bis (benzenesulfonyl) semicarbazide, 4- Toluenesulfonyl semicarbazide, barium azodicarboxylate, 5-phenyltetrazole, trihydrazinotriazine, 4-toluenesulfonyl azide, 4,4′-diphenyldisulfonyl azide and the like. Among these, azodicarbonamide is preferable from the viewpoint of foamability.

  In addition, as the foaming agent, gaseous materials such as gaseous fluorocarbon, nitrogen, carbon dioxide, air, helium and argon, and liquid materials at ordinary temperatures such as liquid fluorocarbon and pentane can be used. Among these, nitrogen and carbon dioxide are preferable from the viewpoint of solubility in resin and foamability.

The blending amount of the foaming agent (C) is 0.01 to 2 parts by mass with respect to 100 parts by mass of the polylactic acid resin composition of the present invention, and preferably 0.05 to 1.5 parts by mass. .
If the blending amount is less than 0.01 parts by mass, the amount of gas to be foamed is small, the resin composition of the present invention cannot be sufficiently foamed, and the apparent density of the resulting foamed molded product cannot be reduced. On the other hand, if the blending amount exceeds 2 parts by mass, the strength of the resulting foamed molded product is reduced, for example, foam breakage occurs during foaming, and appearance defects such as silver streak occur.

  When using the above-described decomposable foaming agent, it is more preferable to use a foaming agent master pellet in which a foaming agent and a thermoplastic resin are mixed. By using the master pellet, the polylactic acid resin and the master pellet are melted together, the foaming agent is easily dispersed, and the foaming gas is efficiently generated in the melted polylactic acid resin, so that the foamability is improved.

  Specific examples of master pellets include pellets obtained by melting and kneading into a thermoplastic resin having a melting point lower than the decomposition start temperature of the foaming agent, mixing the pellets of the thermoplastic resin and the foaming agent powder. And those obtained by compressing and granulating into a shape, and those obtained by mixing and adding a foaming agent to the surface of a thermoplastic resin pellet.

  Examples of the thermoplastic resin used for the master pellet include polyethylene (PE), polystyrene (PS), polypropylene (PP), acrylonitrile styrene (ABS), acrylonitrile styrene (AS), polylactic acid (PLA), polyamide (PA), Polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), polyarylate (PAR), styrene-ethylene-butadiene-styrene (SEBS), ethylene-α-olefin copolymer, ethylene-propylene-diene rubber (EPDM), etc. Can be mentioned.

  It is preferable that 3-50 mass% of a foaming agent is mix | blended with the master pellet mentioned above, and 5-30 mass% is more preferable. If the foaming agent is less than 3% by mass, the foamed molded product obtained with too little foaming agent may not foam sufficiently, or the blended amount of the master pellets may increase, resulting in a decrease in strength of the resulting foamed molded product. is there. On the other hand, when the blending amount of the foaming agent exceeds 50% by mass, the polylactic acid resin composition may be unevenly dispersed in the foaming agent, and foamability may be deteriorated.

  On the other hand, when nitrogen, carbon dioxide, or the like is used as a foaming agent, it is preferable to use these as supercritical fluids, melt and knead them in contact with a polylactic acid resin, and then fill the mold and injection mold.

In order to improve the strength, surface smoothness, and appearance of the foamed molded product, it is preferable that the core part in which the foamed cells exist is covered with a skin part in which the foamed cells do not exist. Such a foam molded article is obtained by, for example, in an injection molding machine, melting a polylactic acid-based resin containing a foaming agent, and injecting it into a mold cavity. The die core part (die plate) adjacent to the core can be obtained by an injection core back type injection molding method in which the thickness of the middle mold cavity is retracted. Here, a value obtained from the receding distance of the die plate and the initial depth of the mold cavity using the following equation is defined as a set foaming ratio (X).
Set foaming ratio (X) = (initial depth + retract distance of die plate) / (initial depth)

  Moreover, the actual foaming ratio (Y) at the time of foam molding can be calculated as a ratio (ρ0 / ρ1) of the density (ρ0) of the unfoamed body and the density (ρ1) of the foamed body. In addition, the density ((rho) 0) of an unfoamed body means the density of a polylactic acid-type resin composition. The actual resin expansion ratio is preferably 1.15 to 6.00 times, and more preferably 1.3 to 4.5 times. When the actual foaming ratio is less than 1.15, the effect of reducing the weight of the obtained foamed molded article is insufficient. On the other hand, when it exceeds 6.00, the foamed cells in the core portion are coarsened in the foamed molded article. In some cases, the skin portion may be thin, and the strength of the foamed molded product tends to decrease.

  The foaming efficiency (Y / X) calculated from the set foaming ratio (X) and the actual foaming ratio (Y) is an index of surface smoothness, preferably 85% or more, and 90% or more. More preferably. When the foaming efficiency (Y / X) is 85% or more, the foamed molded body that foams in the mold increases the adhesion to the mold, and the surface smoothness of the resulting foamed molded body is improved.

The average cell diameter of the foam cells in the core part is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 190 μm or less in order to improve the surface smoothness. If the average cell diameter exceeds 300 μm, the surface smoothness of the foamed molded product may decrease, and the strength of the foamed molded product may decrease.
Further, the thickness of the skin portion is preferably 50 μm or more, and more preferably 100 μm or more. If the thickness of the skin part is less than 50 μm, the strength of the foamed molded product may be lowered.

  The injection-foamed molded article of the present invention has low specific gravity, excellent bending properties, and excellent surface smoothness. Therefore, the injection-foamed molded article is suitably used in daily necessities, electrical / electronic equipment fields, automobile fields, mechanical fields, and the like.

Hereinafter, the present invention will be described more specifically with reference to examples. The measurement and evaluation of various characteristic values in the examples were performed as follows.
(1) D-form content of polylactic acid resin 0.3 g of the obtained resin composition was weighed, added to 6 mL of 1N potassium hydroxide / methanol solution, and sufficiently stirred at 65 ° C. Subsequently, 450 μL of sulfuric acid was added and stirred at 65 ° C. to decompose polylactic acid, and 5 mL was measured as a sample.
To this sample, 3 mL of pure water and 13 mL of methylene chloride were mixed and shaken. After stationary separation, about 1.5 mL of the lower organic layer was collected, filtered through a HPLC disk filter having a pore size of 0.45 μm, and then subjected to gas chromatography measurement using HP-6890 Series GC system manufactured by Hewlett Packard. The ratio (%) of the peak area of D-lactic acid methyl ester to the total peak area of lactic acid methyl ester was calculated, and this was defined as the D-form content (mol%) of the polylactic acid resin.
(2) Melt tension It measured by the said method.
(3) MFR-1 and MFR-2
Measurement was performed by the method described above.

(4) Strain hardening coefficient It measured by the said method.
(5) Crystallization rate index It measured by the above-mentioned method.

(6) Apparent density of injection-foamed molded article Measured and calculated by the above method.
(7) Average cell diameter of injection-foamed molded article The cross section of the obtained injection-foamed molded article was observed for 20 or more bubbles at a magnification of 20,000 using a transmission electron microscope (JEM-200CX manufactured by JEOL). Within the visual field, the major axis diameter of each bubble was visually measured to calculate an average value. This operation was performed in 20 different fields of view, and the average value was calculated as the average bubble diameter.
(8) Bending strength (MPa) of injection foam molding
The obtained injection-foamed molded article was measured according to ASTM D-790.

(9) Surface smoothness of injection-foamed molded article The surface of the obtained injection-foamed molded article was observed, and whether or not the surface had a uniform thickness due to expansion by foaming was visually evaluated in the following three stages. In addition, when foamability is bad, the obtained molded object will be a thing with a nonuniform thickness in the state where the surface wavy.
A: The thickness is uniform and there is no unevenness.
○: Although the thickness is uniform, there is a slight unevenness.
X: Thickness is not uniform.
(10) Heat resistance of injection foam molded article The obtained injection foam molded article was immersed in hot water at 100 ° C for 3 minutes and then taken out. The shape at that time was visually observed and evaluated in the following two stages.
○: Deformation has not occurred ×: Deformation has occurred

〔material〕
<Polylactic acid resin>
A-1: D-form content = 0.4 mol%, weight average molecular weight = 90,000, MFR-1 = 25 (manufactured by Nature Works; 6260D) A-2: D-form content = 0.1 mol%, weight Average molecular weight = 130,000, MFR-1 = 8 (manufactured by Toyota Motor Corporation; S-12)
A-3: D-form content = 1.4 mol%, weight average molecular weight = 90,000, MFR-1 = 25, (manufactured by Nature Works; 6251D)
A-4: D-form content = 1.4 mol%, weight average molecular weight = 130,000, MFR-1 = 8, (manufactured by Nature Works; 3001D)
A-5: D-form content = 1.4 mol%, weight average molecular weight = 160,000, MFR-1 = 3 (manufactured by Nature Works; 4032D)
X-1: D-form content = 10.0 mol%, weight average molecular weight = 130,000, MFR-1 = 10 (manufactured by Nature Works; 6302D)
X-2: D-form content = 4.0 mol%, weight average molecular weight = 160,000, MFR-1 = 4 (manufactured by Nature Works; 4042D)
X-3: D-form content = 0.2 mol%, weight average molecular weight = 70,000, MFR-1 = 35 (obtained by the following method)

[Production of polylactic acid resin (X-3)]
A glass tube was charged with 100 parts by mass of L-lactide and 0.3 part by mass of decanol, and the system was purged with nitrogen. Next, 0.01 parts by mass of tin octylate was added as a polymerization catalyst to 100 parts by mass of L-lactide, and then the temperature was raised to 150 ° C. in a nitrogen atmosphere. When the contents were melted, stirring was started, the internal temperature was further raised to 190 ° C. and polymerization (melt polymerization) was performed for 2 hours, and then the polymerization reaction product was taken out. The obtained polymerization reaction product was vacuum-dried at 130 ° C. for 30 hours to remove lactide remaining in the polymerization reaction product, thereby obtaining a polylactic acid resin (X-3).

<Crystal nucleating agent>
B-1: Talc (Made by Hayashi Kasei Co., Ltd., MW-HST)
B-2: Barium organic sulfonate crystal nucleating agent (manufactured by Takemoto Yushi Co., Ltd .; LAK403)
<Foaming agent>
C-1: Azodicarbonamide (Vinole Hall AC # 3 manufactured by Eiwa Chemical Industry Co., Ltd.)

Production Example 1
100 parts by mass of the polylactic acid resin A-1 was supplied to a twin-screw extruder (Ikegai PCM-30, die diameter: 4 mm × 3 holes, cylinder temperature: 220 ° C., die outlet temperature: 210 ° C.). From the middle of the kneader, 0.1 parts by mass of polyethylene glycol dimethacrylate (Nippon Yushi Co., Ltd.) (abbreviated as PEGDM) and 0.2 parts by mass of dibutyl peroxide (Nippon Yushi Co., Ltd.) (abbreviated as DBPO) were injected. And kneaded. After melt-kneading, a strand is extruded from a 0.4 mm diameter × 3 hole die, cut into a pellet, and is dried at a temperature of 60 ° C. with a vacuum dryer (trade name “Vacuum Dryer DP83” manufactured by Yamato Kagaku). What was dried for 48 hours was designated as crosslinked polylactic acid resin K-1.

Production Examples 2-7, 9-12
Crosslinked polylactic acid resins K-2 to K-7 and K-9 to K-12 were obtained in the same manner as in Production Example 1, except that the ratios of various components were changed to those shown in Table 1.

Production Example 8
100 parts by mass of polylactic acid resin A-2 was supplied to a twin screw extruder (Ikegai PCM-30, die diameter: 4 mm × 3 holes, extrusion head temperature: 200 ° C., die outlet temperature: 180 ° C.). Using a pump from the middle of the kneader, 0.5 part by weight of PEGDM and 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-tripaoxonan ("Trigonox 301" manufactured by Kayaku Akzo) ]) 0.5 parts by mass were injected and melt-kneaded. After melt-kneading, a strand is extruded from a 0.4 mm diameter × 3 hole die, cut into a pellet, and is dried at a temperature of 60 ° C. with a vacuum dryer (trade name “Vacuum Dryer DP83” manufactured by Yamato Kagaku). What was dried for 48 hours was designated as crosslinked polylactic acid resin K-8.

Example 1
Using 2 parts by mass of the crystal nucleating agent B-1 with respect to 100 parts by mass of the crosslinked polylactic acid resin K-1 obtained in the above production example, these were dry blended and a twin screw extruder (TEM26SS manufactured by Toshiba Machine Co., Ltd.). The mold was melt-kneaded under the conditions of a barrel temperature of 190 ° C., a screw rotation speed of 150 rpm, and a discharge of 15 kg / h. After melt-kneading, a strand is extruded from a 0.4 mm diameter × 3 hole die, cut into a pellet, and is dried at a temperature of 60 ° C. with a vacuum dryer (trade name “Vacuum Dryer DP83” manufactured by Yamato Kagaku). The polylactic acid resin composition was obtained by drying for 48 hours.
Next, with respect to 100 parts by mass of the obtained polylactic acid-based resin composition, 0.5 parts by mass of the foaming agent C-1 was used, and these were dry blended to produce an injection molding machine (S-2000i type manufactured by FANUC). And injection molding was performed. Injection molding was performed at a cylinder temperature of 200 ° C and a mold temperature of 100 ° C. For injection molding, a mold having a cavity having a length of 127 mm, a width of 12.7 mm, and a depth of 1.6 mm was used. Here, the initial thickness of the foamed molded product is 1.6 mm, and the die plate is retracted so that the set foaming ratio is 2.5 times to obtain an injection foamed molded product composed of a core layer and a skin layer. It was.

Examples 2-14, Comparative Examples 1-7
A polylactic acid resin composition was obtained in the same manner as in Example 1 except that the types and ratios of the crosslinked polylactic acid resin and the crystal nucleating agent were variously changed as shown in Table 2.
And using the obtained polylactic acid-type resin composition, injection molding was performed like Example 1, and the injection foaming molding was obtained.

  Table 2 shows the characteristic values and evaluations of the polylactic acid resin compositions and the injection-foamed molded articles obtained in Examples 1 to 14 and Comparative Examples 1 to 7.

Examples 15-17
Example 1 except that the polylactic acid-based resin composition obtained in Example 2 was used and the die plate was retracted so that the set foaming ratio was 1.5 times, 3 times, and 5 times during injection molding. Similarly, an injection foam molded article was obtained.

Example 18
Using the polylactic acid-based resin composition obtained in Example 5, the injection foam molded article was obtained in the same manner as in Example 1 except that the die plate was retracted so that the set foaming ratio was 3 times at the time of injection molding. Obtained.

  Table 3 shows the characteristic values and evaluations of the injection-foamed molded articles obtained in Examples 15 to 18.

  As is clear from Tables 2 and 3, the polylactic acid-based resin compositions obtained in Examples 1 to 14 had the performance specified in the present invention, and therefore are suitable for injection foaming. Good foaming was achieved even when the set foaming ratio was 2.5. The injection-foamed molded articles of Examples 1 to 18 obtained from these resin compositions have a small average cell diameter, excellent surface smoothness, and excellent bending strength and heat resistance. It was. For this reason, it was able to be used suitably for various uses, such as electrical and electronic equipment parts and a molded article for miscellaneous goods.

  On the other hand, the polylactic acid-based resin compositions obtained in Comparative Examples 1 to 3 did not satisfy the conditions (1) to (3) of the present invention because the crosslinked polylactic acid resin was not used. An injection foam molded article could not be obtained. Since the polylactic acid-based resin composition obtained in Comparative Example 4 did not satisfy the condition (1) of the present invention, the resin did not stretch and an injection foam molded article could not be obtained. Since the polylactic acid resin compositions obtained in Comparative Examples 5 and 6 had a D-form content of the polylactic acid resin (A) exceeding 2 mol%, the injection foamed foams obtained from these resin compositions The molded body was inferior in heat resistance. Since the polylactic acid resin composition obtained in Comparative Example 7 did not satisfy any of the conditions (1) to (3) of the present invention, the resin was cut or torn during foam molding. The injection-foamed molded article had a large cell diameter, and both surface smoothness and bending strength were inferior.

Claims (5)

A polylactic acid resin composition for injection foaming, characterized in that a polylactic acid resin (A) having a D-form content of 2 mol% or less is a main component and the following conditions (1) to (3) are simultaneously satisfied.
(1) The melt tension measured at 190 ° C. is 20 to 200 mN.
(2) The melt viscosity (MFR-1) measured at 190 ° C. and 21.6 N is 0.1 to 20 g / 10 min, and the melt viscosity (MFR) measured at 190 ° C. and 132.25 N is used. -2) (MFR-2 / MFR-1) is 15 or more.
(3) In the time-elongation viscosity curve obtained by the extensional viscosity measurement at a temperature 10 ° C. higher than the melting point, the slope a1 of the linear region at the initial stage of elongation until the inflection point appears and the slope a2 of the later stage of elongation after the inflection point The ratio (a2 / a1, strain hardening coefficient) is 1.2-20. The polylactic acid resin composition for injection foaming according to claim 1, wherein the crystallization rate index is 0.1 to 10 (min). The crystal nucleating agent (B) is contained in an amount of 0.5 to 50 parts by mass with respect to 100 parts by mass of the polylactic acid resin (A) having a D-form content of 2 mol% or less. The polylactic acid resin composition for injection foaming according to claim 1 or 2, wherein the composition is at least one selected from talc, silica, layered silicate, glass fiber, and organic crystal nucleating agent. An injection foamed molded article comprising the polylactic acid resin composition for injection foaming according to any one of claims 1 to 3, and an apparent density of 1.1 g / cm ³ or less. Injection molding is performed after containing 0.01 to 2 parts by mass of the foaming agent (C) with respect to 100 parts by mass of the polylactic acid resin composition for injection foaming according to any one of claims 1 to 3. A method for producing an injection foam molded article.